Microdialysis sampling with on-line microbore HPLC for the determination of tirapazamine and its reduced metabolites in rats

An on-line microdialysis microbore HPLC method is described for the determination of the bioreductive anti-tumor agent, tirapazamine (3-amino-1,2,4-benzotriazine-1,4-di-N-oxide, SR4233, WIN59075, Tirazone, TPZ) and its two major reduced metabolites, 3-amino-1,2,4-benzotriazine-1-N-oxide (SR4317) and 3-amino-1,2,4-benzotriazine (SR4330). Detection limits of 0.003 mu M, 0.005 mu M and 0.007 mu M were obtained for tirapazamine, SR4317 and SR4330, respectively. Linear ranges of 0.011-20 mu M, 0.017-20 mu M and 0.025-20 mu M for tirapazamine, SR4317 and SR4330 permitted quantitative analysis of all three compounds in microdialysis samples. Typical intra-day reproducibilities (n = 7) of 4.1% (tirapazamine), 6.6% (SR4317), 9.9% (SR4317), and 1.8% (tirapazamine), 2.4% (SR4317) and 2.6% (SR4330) were obtained at the 0.12 mu M and 1.2 mu M levels, respectively. Inter-day reproducibilities (n = 5) of 3.4% (tirapazamine), 1.8% (SR4317), 4.5% (SR4330) and 2.5% (tirapazamine), 2.5% (SR4317) and 1.7% (SR4330) were obtained at the 0.12 mu M and 1.2 mu M levels, respectively. The use of an on-line microdialysis HPLC system, permitted the determination of tirapazamine, SR4317 and SR4330 in blood and muscle tissue of rats with a high temporal resolution of sampling. The pharmacokinetics of tirapazamine and its metabolites were studied in the muscle and blood of rats previously administered an intraperitoneal dose of tirapazamine.